A plastic display, such as an electrophoretic display, typically comprises two electrodes, at least one of which is patterned, and a display medium layer. Biasing voltages typically are applied selectively to the electrodes to control the state of the portion(s) of the display medium associated with the electrodes being biased. For example, a typical passive matrix electrophoretic display may comprise an array of electrophoretic cells arranged in rows and columns and sandwiched between a top and bottom electrode layer. The top electrode layer may comprise, for example, a series of transparent column electrodes positioned over the columns of electrophoretic cells and the bottom electrode layer may comprise a series of row electrodes positioned beneath the rows of electrophoretic cells. Several types of passive matrix electrophoretic displays are described in U.S. Provisional Patent Application Ser. No. 60/322,635 entitled “An Improved Electrophoretic Display with Gating Electrodes,” filed Sep. 12, 2001, U.S. Provisional Patent Application Ser. No. 60/313,146 entitled “An Improved Electrophoretic Display with Dual mode Switching,” filed on Jul. 17, 2001, and U.S. Provisional Patent Application Ser. No. 60/306,312 entitled “An Improved Electrophoretic Display with In-Plane Switching,” filed on Aug. 17, 2001, all of which are hereby incorporated by reference for all purposes.
One typical prior art approach to fabricating the patterned electrode layer(s) for such a plastic display typically involves the use of photolithographic techniques and chemical etching. Conductor films useful for plastic display applications may be formed by a process such as laminating, electroplating, sputtering, vacuum deposition, or combinations of more than one process for forming a conductor film onto a plastic substrate. Useful thin film conductors include metal conductors such as, for example, aluminum, copper, zinc, tin, molybdenum, nickel, chromium, silver, gold, iron, indium, thallium, titanium, tantalum, tungsten, rhodium, palladium, platinum and/or cobalt, etc., and metal oxide conductors such as indium tin oxide (ITO) and indium zinc oxide (IZO), as well as alloys or multilayer composite films derived from the aforementioned metals and/or metal oxides, e.g., aluminum zinc oxide, gadolinium indium oxide, tin oxide, or fluorine-doped indium oxide. Further, the thin film structures described herein may comprise either a single layer thin film or a multilayer thin film. ITO films are of particularly interest in many applications because of their high degree of transmission in the visible light region. Useful plastic substrates include epoxy resins, polyimide, polysulfone, polyarylether, polycarbonate (PC), polyethylene terephthalate (PET), polyethylene terenaphthalate (PEN), poly(cyclic olefin), and their composites. The conductor-on-plastics films are typically patterned by a photolithographic process which comprises several time consuming and high cost steps including (1) coating the conductor film with photoresist; (2) patterning the photoresist by image-wise exposing it through a photomask to, for example, ultraviolet light; (3) “developing” the patterned image by removing the photoresist from either the exposed or the unexposed areas, depending on the type of photoresist used, to uncover the conductor film in areas from which it is to be removed (i.e., areas where no electrode or other conductive structures is to be located); (4) using a chemical etching process to remove the conductor film from the areas from which the photoresist has been removed; and (5) stripping the remaining photoresist to uncover the electrodes and/or other patterned conductive structures.
For mass fabrication of a plastic display, such as an electrophoretic display, it may be advantageous to employ a continuous roll-to-roll process. However, the photolithographic approach described above is not well suited to such a roll-to-roll process, as certain of the processing steps, such as the image-wise exposure, are time consuming and require careful registration and alignment of the mask and the moving target area. In addition, development and stripping of photoresist and treatment of waste from the chemical etching process may be time consuming and expensive, in addition to potentially posing an environmental hazard.
Therefore, there is a need for a process for forming patterned conductive structures on a plastic substrate, for use in a plastic display such as an electrophoretic display, that does not require the use of photolithography or chemical etching and that is suitable for use in a continuous roll-to-roll process.